Composite carbonaceous members for furnace rolls and other high temperature members



United States Patent 3,352,549 COMPOSITE CARBGNACEOUS MEMBERS FOR FURNACE ROLLS AND OTHER HIQH TEM- PERATURE MEMBERS Martin N. Ornitz, Wilkinsburg, and Ray H. English, McCandless Township, Allegheny County, Pa., assignors to Blaw-Knox Company, Pittsburgh, Pa., a corporation of Delaware N0 Drawing. Filed Oct. 29, 1964, Ser. No. 407,516 19 Claims. (Cl. 263-6) This invention relates to composite carbonaceous members for furnace rOlls and other high temperature members and particularly to composite carbonaceous members consisting essentially of carbon and metal and boron compounds to serve as work-engaging sunface elements of furnace conveyor units and the like, and, the method of producing such members. More particularly, this invention relates to such composite members and method for furnace rolls and other conveyor units to su portably engage metal work at elevated temperatures which may contain reactive oxygen in the atmosphere thereof, to inhibit pick-up by the metal work and/ or the conveyor ele ments, and, to inhibit oxidation deterioration of such members in such atmosphere.

The heat treating of aluminum strip and its alloys is usually performed in an intermediate temperature furnace, which may be around 1000 F., in an air atmosphere. Such air contains such large quantities of oxygen as to be deleterious to carbon-and-metal furnace conveyor members covered by United States Letters Patent No. 3,03 7,756 issued to the assignee hereof; and in those members in which boron oxide was added in accordance with that patent, the furnace temperature at such an intermediate level appears to cause the boron oxide to be relatively inert, thereby decreasing its ability to act as a promoter to enhance the mechanical strength and resistance of such carbon-and-metal members.

Vie have discovered that the work-engaging members for furnace rolls and other conveyor units may be made of a bonded, shaped composition consisting essentially of carbon, a selected metal and a boron compound other than boric oxide, for example, boron carbide (B C), which are not subject to the nace having an air atmosphere and/or an intermediate heat treating temperature (up to about 1200 F.) such as that suitable for the heat treating of aluminum strip and its alloys, together with a preferred method for producing such members. In addition, we have found such carbon-metal-boron compound members may be satisfactorily used in higher temperature protective atmosphere furnaces for the heat treating of steel and other relatively high strength metals and alloys. Such members in all cases inhibit pick-up by the metal work supportably engaged thereby and/or the members themselves, While at the same time resisting carbon loss deterioration, dimensional change and wear. Such members of this invention may be molded and used as work-engaging roll sleeves, relatively flat or otherwise shaped members for the surfacing of conveyor units in ways illustrated in the aforesaid Letters Patent. Further, members of this invention may be utilized in continuous strip furnaces, roller hearth furnaces and other types of continuous and noncontinuous furnaces for the heat treating of metal work while inhibiting pickup on the work or members and oxidation deterioration of such members. In addition, the composition of this invention may be used in forming missile parts, refractory brick, structural members, etc. which are subject to high temperatures.

Starting materials for the composition of a workengaging member of this invention consist essentially of a boron com ound other than boric oxide, a preferential affinity metal, with the balance substantially carbon.

deleterious effects of a furi The boron compound may be boron carbide, boron nitride, elementary boron, titanium diboride, zirconium dihoride, and the like. Boric oxide is not satisfactory because it makes the carbon bond discontinuous and the material softens at high temperature. We prefer to use boron carbide because it is readily obtainable as such in powder form and commercial grade. The preferential aflinity metal for such work-engaging member consists of silicon, titanium, zirconium, chromium and alloys and metal mixtures thereof in which one of such named metals predominates. By preferential afi'inity metal as used herein is meant a metal which forms a stable solid predominantly non-alkaline oxide with a melting point not lower than the expected furnace temperature which has afiinity for reaction available oxygen higher than the afiinity which carbon has for oxygen at the heat treating temperature which will prevail in the particular furnace in which the member is used. Such a preferential afiinity metal herein may be a substantially commercially pure metal, an alloy thereof, or a metal mixture of such preferential affinity metals. The carbon in the work-engaging member composition of this invention may be graphitic or non-graphitic carbon and initially contain a suflicient quantity of a binder such as pitch, resins and synthetic resins such as phenol formaldehyde and fur furyl alcohol or tar to be carbonized during the heat curing of the member to bond its ingredients together in the desired shape for use.

In preparing a bonded and carbonized workengaging member of this invention, such boron carbide, preferential aflinity metal and carbon including the binder, are mixed together, molded into the desired shape which the new member is to have and heated to a carbonizing temperature in a known manner and by known means, which carbonizing as such is not a part of this invention, in a selected atmosphere to a carbonizing temperature for a predetermined time to cure the molded member and provide the bonded work-engaging member.

A preferred range of the composition ingredients for a work-engaging member of this invention consists essentially of, in terms of weight percentage based on the total weight-boron compound up to about 30%; one or more of such preferential ailinity metals inclusive of alloys and/ or mixtures thereof in which one or more of such preferential afiinity metals collectively predominate, in an amount of from about 1% to about 50%; with the balance substantially carbon including the canbonized binder. A preferred composition for a work-engaging member of this invention consists of boron carbide in a weight percentage amount from about 1% to about 20%; a preferential ai'rinity metal, such as silicon, in a weight percentage in the neighborhood of about 25%; with the balance consisting essentially of carbon, which in turn may consist of a binder pitch including tar or a resin in the neighborhood of from about 20% to about 30% by weight, plumbago in the neighborhood of from about 5% to about 10% by weight and petroleum coke or other solid carbon particles in the neighborhood of the balance by weight. When more boron carbide is added, it may be at the expense of carbon. Moreover, it has been found that boron compounds such as boron car-bide are relatively stable, forming only glazing amounts of boron oxide, in the presence of such water vapor at furnace temperatures at which reactive oxygen therefrom will be present in the air or non-air atmosphere used in such furnace.

We have also discovered that when a work-engaging member of this invention is to be utilized in a furnace operated at an intermediate temperature level, which may be one up to, say, 1200 F., a pretreatment of the bonded hardened work-engaging member is essential. A preferred I mode of pretreatment consists in heating such bonded,

phere produced by burning seven volumes of air with 5 one volume of natural gas, the effluent combustion products comprising the atmosphere and being one of the socalled forms of DX atmospheres. Without being limited to this explanation, it appears that such preliminary treatment tends to form a coating of boron oxide on the sur- 1O face of the carbon particles and inhibit movement of oxygen along carbon surfaces and prevents premature reaction and breakdown of the work-engaging member in an air atmosphere furnace at or near such an intermediate temperature level such as might be used for aluminous 15 metal, often heat treated at about 1000" F., and/ or other non-ferrous metal work. No such pretreatment is necessary when the furnace temperature is in the neighborhood of 1200 F. and above for the heat treating of metal work in a protective atmosphere containing free oxygen or re- 20 active oxygen-containing gas.

Laboratory tests show marked advantages obtainable by work'engaging members of this invention. Therein, the furnace used was a mufile furnace. Small, solid cylinders comprised the test samples and the atmosphere present 25 in the furnace on the outside of the mufiie reached all surfaces of each test sample. The test sample designated as A in each of the Test Groups I and II had a composition covered by the aforesaid Letters Patent No. 3,037,-

756. The other test samples in both groups of tests had 30 compositions of the instant invention. All samples were of compositions which inhibit pick-up. In Test Group I, an air atmosphere was used in the sample space of the laboratory furnace outside of the muffie and that air was blown through such space at relatively high velocity in the neighborhood of 2500 feet per minute by a fan while Such results demonstrate marked advantages achievable by carbon-metal-boron carbide compositions of and members produced in accordance with this invention. Such members have full anti-pick-up and oxidation inhibiting qualities with dimensional stability and resistance to wear Without being subject to excessive deterioration in air atmospheres, or at intermediate temperature levels. Further, the promoter quality of the boron atom in transferring from the carbide to the oxide form in the course of use under this invention, as appears to be the case, can be increased hereunder in that greater quantities thereof can readily be incorporated in compositions of this invention without any adverse effect upon the bonding of the ingredients during carbonizing to form a Work-engaging member of this invention.

Sets of test bars for a silicon line were made according to the present invention and according to the best prior art known to applicants. The two sets of rolls had the following composition.

Prior art Percent Si 25 Graphite 59 Carbon bond 15 B l Invention Si s 25 Graphite 59 Carbon bond 11 B C 5 The bars were inserted for a 24 hour period at 1800 F. :20 at a dew point of 125 F. in an atmosphere of 7% CO 8.5% CO, 11% H and the remainder N maintaining the furnace temperature and the temperature Pri Art Inventmn of the sample at about 1000 F. In Test Group II, a reac rive oxygen-containing atmosphere, substantially non- 40 Original we, gms 57.0102 75.3906 clrculatmg m character, a utilized at a higher heat Final gms 530396 M1827 treatment fur ace perating temperature (about 1800 LOSS, gms 9766 2079 1 l 2 F.) such as might be used in heat treating Steels and Vafl- X'iiiii l1; 0 017 512 5 in 2 0 fiogzgrilgsglin ous hlgh temperature alloy metals. Results of such tests Gondltlon and powdery Hard intact were: 45 around edges I.Labor atory Tests0xidation Resistance in Air I Weight Chan Test Composition (weight percent) in./l1r.) a l: 1,0 ri0 ii n 1 fii 1 i Samples Velocity Air cgggige Silicon Carbon (a) 100 hrs. (b) 98 hrs. (0) 100 hrs.

5 25 70 0000s 0000i 10 z e5 00507 00049 0077 2a 00 00350 00039 003 55 00304 00031 000? 25 25 50 00385 00029 0044 2s 45 0002 00008 0038 25 00103 +.0001s 0045 1 Sample A impregnated with boron oxide (about 1 b w 2 Sample 4 had become powder at the end of the f est tiib ggl gm 1 regaiifipd surhlcren't hardness to be used as a structural material 1 p es samp es excep were given a preliminar hours at 1,800 F. in a 7 air-1 natural gas (DX) atmo sp eig for 4 II.Oxidation Resistance irkfiAir Corrosion Atmosphere (10 Air-1 atural Gas) The foregoing results illustrate the remarkable superiore ght LOSS Rate ity of the composi tion of the present invention over prior Test samples gg ?t% 7% F art materials, particularly at high dew points.

dewpointi for 100 h i A like set of bars were tested at 2025i20 F. for 24 hours in an atmosphere of 7.3:1 air to natural gas plus 11:23:33: I: added CO to produce 10% CO, the final atmosphere being 7.5% CO 10% CO, 9.2% H and the remainder N 1 NB. Samples A and B in Test Group II had the same respective compositions as Samples A and B in Test Group 1; however, there was no preliminary pretreat ment of Sample B in Test Group II.

Samples were removed at the end of the test period and compared as in the preceding case with the following 7 results Prior Art Invention Initial Vt, gms-- 58. 4758 39. 8331 Final Wt, gms- 51. 4934 38. 8316 Wt. Loss, gms 6. 9824 1. 0015 Surface Area, in. 5. 508 6. 530 Wt. Loss/Surface Area, gm./ 1. 268 0. 153

Condition Soft, powdery Hard, intact A roll was made according to the present invention having the following composition:

Percent Si 25 Graphite 59 3 C 5 Carbon bond 11 8. A work-engaging member to engage metallic work for a heat treating furnace conveyor unit and the like, comprising, in combination, carbon, metal and boron carbide in shaped, bonded admixture, the weight of metal therein being in the neighborhood of 25 %'by weight, the weight of boron carbide therein being in the neighborhood of from about 5% to about 25% by weight, the weight of carbon therein being in the neighborhood of from about 70% to about 55% by weight, said metal being selected from the group consisting of silicon, titanium, zirconium, chromium and alloys and metal mixtures thereof in which at least one of said named metals predominates.

9. Composition for composite members of a furnace conveyor unit and the like to engage metallic work in a heat treating furnace, comprising, in combination, carbon, metal and boron carbide in shaped, bonded admixture, the weight of metal therein being in the range of from about 1% to about by weight, the weight of boron carbide being in the range of from about 1% to about 35% by weight, the balance consisting essentially of carbon in an amount suflicient to inhibit pick-up, said metal further having a preferential afiinity for reactive oxygen in the furnace atmosphere gases relative to carbon at furnace temperatures, the ability to form stable solid predominantly non-alkaline oxide and to inhibit sub- Invention Round Graphite Slab Graphite Vt. Change- 0.03920 grn./in. /hr -0.10070 gm./in. /hr -0.07370 gnL/inJ/hr. Condition Hard, intact Disintegrated, bond Disintegrated, bond destroyed.

destroyed.

The foregoing tests illustrate the remarkable improvement of the composition of this invention over prior art materials in the environment in which it is designed to supplant such earlier materials.

The foregoing disclosure and description is by way of illustration and not by way of limitation and it is understood that a practice of our invention may be otherwise embodied and practiced within the scope of the following claims.

We claim:

1. Composition for composite members to engage metallic work for a heat treating furnace conveyor unit and the like, comprising, in combination, an admixture of carbon and metal and boron compounds other than boron oxide, the weight of metal therein being in the neighborhood of 25 by weight, the weight of boron compound therein being in the neighborhood from about 1% to about 20% by weight, the balance consisting essentially of carbon, said metal being selected from the group consisting of silicon, titanium, zirconium, chromium and alloys and metal mixtures thereof in which at least one of said named metals predominates.

2. Composition as set forth in claim 1 in which said carbon consists of in the neighborhood of from about 5% to about 10% of plumbago by weight, from about 15% to about 30% by weight of a carbonaceous material selected from the group consisting of pitch and resins and the balance coke, said percentages by weight being based upon the total weight of said admixture.

3. Composition as set forth in claim 1 in which said metal is silicon and alloys and metal mixtures thereof in which silicon predominates.

4. Composition as set forth in claim 1 in which said metal is titanium and alloys and metal mixtures thereof in which titanium predominates.

5. Composition as set forth in claim 1 in which said metal is zirconium and alloys and metal mixtures thereof in which zirconium predominates.

6. Composition as set forth in claim 1 in which said metal is chromium and alloys and metal mixtures thereof in which chromium predominates.

7. Composition as set forth in claim 1 wherein the boron compound is boron carbide.

stitution for boron in boron carbide at such temperatures.

10. Composition for support members to engage metallic work at reactive temperatures being a bonded admixture of boron carbide in an amount not to exceed 30% by weight, at least one metal characterized by its preferential atlinity relative to carbon at such temperatures for any free oxygen and reactive oxygen-containing gases present, the ability to form stable solid predominantly non-alkaline oxide in any of such gases and its not being subject to replacing boron in said boron carbide, said oxide having a melting point not lower than such temperatures, said metal being in a sufficient quantity not to exceed 50% by weight to inhibit deterioration of such member in any such gases, with the balance of said admixture being substantially carbon.

11. Composition for a support member as set forth in claim 9 in which said metal is silicon.

12. Composition for a support member as set forth in claim 9 in which said metal is titanium.

13. Composition for a support member as set forth in claim 9 in which said metal is zirconium.

14. Composition for a support member as set forth in claim 9 in which said metal is chromium.

15. Process for making composite carbonaceous members for furnace rollers and the like to inhibit deterioration and pick-up, comprising, in combination, admixing a metal selected from the group consisting of silicon, titanium, zirconium, chromium and alloys and metal mixtures thereof in which at least one of said named metals predominates in the range of from about 1% to about 50% by weight, boron compounds other than boron oxide in the range of from about 3% to about 30% by weight, and a balance by weight consisting essentially of carbon inclusive of at least about 15 by weight of binder, shaping and carbonizing said admixture to bond the same in shaped form, heating said admixture in a protective atmosphere to a temperature at least above about 1200 F. for a period of at least four hours, and using said bonded shaped admixture in an intermediate temperature furnace to engage metallic work in the presence of any reactive oxygen-containing atmosphere including air.

16- Process for making composite carbonaceous members for furnace conveyor units and the like to engage metallic work, comprising, in combination, admixing a metal in the range of from about to about 35% by weight and selected from the group consisting of silicon, titanium, zirconium, chromium and alloys and metal mixtures thereof in which at least one of said named metals predominates, boron carbide in an amount up to about 25% by weight, and a balance consisting essentially of carbon inclusive of at least about by weight of binder, shaping and carbonizing said admixture to bond the same, and heating said admixture in a protected atmosphere to a temperature at least above about 1200 F. for a period of time sufficient to form a slight glaze on the surface thereof, and using said bonded shaped admixture in a furnace to engage metallic work in the presence of a reactive oxygen-containing atmosphere.

17. Composition for composite members subject to high temperatures comprising, in combination, an admixture of carbon and metal and boron compounds other than boron oxide, the weight of metal therein being in the neighborhood of by weight, the weight of boron compound therein being in the neighborhood from about 1% to about 20% by weight, the balance consisting essentially of carbon, said metal being selected from the group consisting of silicon, titanium, zirconium, chromium and alloys and metal mixtures thereof in which at least one of said named metals predominates. I

18. Composition for composite members subject to high temperatures comprising carbon, metal and boron carbide in shaped, bonded admixture, the weight of metal therein being in the neighborhood of 25% by weight, the weight of boron carbide therein being in the neighborhood of from about 5% to about 25% by weight, the weight of carbon therein beingin the neighborhood of from about 70% to about 55% by Weight, said metal being selected from the group consisting of silicon, titanium, zirconium, chromium and alloys and metal mixtures thereof in which at least one of said named metals predominates.

19. Composition for composite members subject to high temperatures comprising, in combination, carbon, metal and boron carbide in shaped, bonded admixture, the Weight of metal therein being in the range of from about 1% to about 50% by weight, the weight of boron carbide being in the range of from about 1% to about by Weight, the balance consisting essentially of carbon in an amount sufiicient to inhibit pick-up, saidtmetal further,

having a preferential aflinityr for reactive oxygen in the furnace atmosphere, gases relative to carbon at furnace temperatures, the'ability to form stable solid predominantly non-alkaline oxide and to inhibit substitution for boron in boron carbide at such temperatures.

References Cited UNITED STATES PATENTS 3,037,756 6/1962 Ornitz 263-6 3,174,372 3/1965 Fisher et al l0656 3,199,993 8/1965 Schre'welius 106-56 X FREDERICK L. MATTESON, IR., Primary Examiner.

D. A. TAMBURRO, Assistant Examiner. 

1. COMPOSITION FOR COMPOSITE MEMBERS TO ENGAGE METALLIC WORK FOR A HEAT TREATING FURNACE CONVEYOR UNIT AND THE LIKE, COMPRISING, IN COMBINATION, AN ADMIXTURE OF CARBON AND METAL AND BORON COMPOUNDS OTHER THAN BORON OXIDE, THE WEIGHT OF METAL THEREIN BEING IN THE NEIGHBORHOOD OF 25% BY WEIGHT, THE WEIGHT OF BORON COMPOUND THEREIN BEING IN THE NEIGHBORHOOD FROM ABOUT 1% TO ABOUT 20% BY WEIGHT, THE BALANCE CONSISTING ESSENTIALLY OF CARBON, SAID METAL BEING SELECTED FROM THE GROUP CONSISTING OF SILICON, TITANIUM, ZIRCONIUM, CHROMIUM AND ALLOYS AND METAL MIXTURES THEREOF IN WHICH AT LEAST ONE OF SAID NAMED METALS PREDOMINATES. 